mattdb9

When idling my alternator is not charging. I have replaced it and it is still doing the same. I took the old alternator to autozone to have it checked, on their machine and it passed. I have had my battery checked twice and it is fine. After that I begin looking for other answers. I checked my ground wire and it seemed that it was a little loose, thought that might have been the problem but it is still doing the same. I am running about 800rpm idling when in park to 700 when in gear and on brake. My belt is tight. I am all out of answers or causes. Do you think it is wiring? If so where do I start or how expensive would that be to take it somewhere? Also I did buy a rebuilt alternator and when they tested both alternators they just did so at one speed, which seemed to be pretty fast. Its charges fine when I rev my engine or drive. Should I try another new one? Is it ok to drive temporary or would this hurt something else. '97 camaro Z28

dhdenney

iTrader: (53)

Do you have any mods like underdrive pulley?

mattdb9

I just bought it about three months ago. The guy told me he had oversized pulleys on it, but thats all I know. However it recently started doing this.

dhdenney

iTrader: (53)

Bought the car 3 months ago? They don't make "oversized" pullies.

mattdb9

sorry yes, just bought the car. I can't remeber what he said but I remember something about diff. pulleys.

dhdenney

iTrader: (53)

Sounds like the problem. You have an underdrive pulley. Take that off and you should be golden.

Formula350

iTrader: (3)

They make oversized Alternator pullies I thought, for when you do underdrive crank....

dhdenney

iTrader: (53)

I guess I should have said I don't think they make oversized pullies for the LT1 but I think I have seen them for the TPI's. If they do make an oversized pulley for the LT1, show us a link, I don't think I have ever seen any.

1SLO6

iTrader: (8)

check the wire coming off the back of the alternator the heavy gauge wire.... make sure it is not cracked, burnt or stiffer than any other wire. mine was doin the same.... checked that wire and found that it was a little fried. remember as the car gets old wires do to just make sure all your output and inout vooltages are ok and u should be fine. its just an older car.

Ralls

iTrader: (32)

Like dhdenney caught on, it's probably the under drive pulleys. It makes the accessories run slower, including the alternator. It won't charge unless it's somewhere above 900rpm with those pulleys. Go back to stock pulleys or get a bigger alternator pulley if they make them (?).

1994Z28Lt1

iTrader: (1)

everyone is mistaken in order to increase the speed of the alternator you must decrease the size of the alternator pulley in relation with the crank pulley

thinks of gear ratios

if you have a crank pully that is 5 inches and an alternator pulley of one inch you are overdriving the alternator at a 5:1 ratio

so for every 1000 rpm of crank rotation the alternator spins 5000 rpm

if you go with a larger alternator pulley such as one that is 2.5 inches than you are only overdriving the alternator at a 5:2.5 ratio so for every 1000 rpm of crank rotation you spin the alternator 2500 rpm

so in other words you need a smaller alternator pulley

koolaid_kid

iTrader: (21)

They did make them; I bought one years ago. But the company I purchased mine from, Internet Racer's Supply, went out of business years ago.

dhdenney

iTrader: (53)

That does make sense, sir. I just indicated that they don't make "oversized" pulleys for the LT1, however. I think the original poster's best bet would be to just go back to stock.

chromeplated500

iTrader: (10)

I would check the actuater wire. the one that hooks on the side of the Alt. it pretty much tells it when to start charging. and check/clean up your grounds. underdrive/overdrive??? pullies arent goint to make you r car not charge.

dhdenney

iTrader: (53)

Yes an underdrive pulley will slow down the alternator, all else constant. See 1994Z28Lt1's post above.